Cholesterol affects the relationship between albumin and major adverse cardiac events in patients with coronary artery disease: a secondary analysis

We aimed to examine whether the efficacy of the risk of poor prognosis in patients with coronary artery disease is jointly affected by total cholesterol and baseline serum albumin in a secondary analysis of previous study. We analyzed the data of 204 patients from October 2014 to October 2017 for newly diagnosed stable CAD. The outcome was major adverse cardiac events (MACE; defined as all cause mortality, non fatal myocardial infarction, and non fatal stroke). The median duration of follow-up was 783 days. Multivariable COX model was performed to revalidate the relationship between the sALB and MACE and interaction tests were conducted to find the effects of total cholesterol on their association. A total of 28 MACE occurred among the 204 participants. The risk of MACE varied by baseline serum albumin and total cholesterol. Specifically, lower serum albumin indicated higher risk of MACE (HR 3.52, 95% CI 1.30–9.54), and a test for interaction between baseline serum albumin and total cholesterol on MACE was significant (P = 0.0005). We suggested that baseline serum albumin and total cholesterol could interactively affect the risk of poor prognosis of patients with coronary artery diseases. Our findings need to be confirmed by further randomized trials.


Statistical interaction between sALB and TC on MACE.
presents the association between sALB level and the risk of MACE (logHR), stratified by TC. The solid line, which represents those whose TC less than 200 mg/dL, shows a decline in MACE risk with increasing sALB level after adjusting for covariates. Contrarily, there is no such association in those whose TC more than 200 mg/dL. Because of sample size limitation, our primary outcomes were the tests for interaction between sALB and TC on MACE. The result was statistically significant in crude model (P = 0.0005), and compared with crude model, the effect of TC on the relationship between sALB and MACE did not change markedly after adjusting for age, sex, BMI, ALT, eGFR in the multivariable analysis (P = 0.0005) ( Table 3).

Discussion
As some previous studies reported, baseline TC and sALB seem to be risk factors of poor prognosis in CAD patients. We conducted this study mainly to explore whether there is an interaction between them. We analyzed the interaction between TC and sALB and adjusted for covariates that may have influenced the results based on literature reports and clinical practice. Our analysis showed an interaction between TC and sALB levels after adjusting for covariates, which may suggested that baseline TC may influence the effect of sALB on the risk of poor prognosis in patients with coronary artery disease undergoing percutaneous coronary intervention. The relationship between sALB and cardiovascular risk has ever been reported by some previous studies. The study by Suzuki et al. suggested that the baseline sALB was a risk factor of long-term MACE in patients undergoing PCI 15 . Shih-Chieh Chien et al. pointed out that sALB is one of the reliable risk factors of CVD prognosis 16 . Oduncu et al. retrospectively analyzed 1706 patients with ST-segment elevation myocardial infarction (STEMI) who underwent PCI and suggested that lower sALB was independent risk factor of long-term mortality 17 . The potential mechanisms linking TC with sALB in cardiovascular prognostic risk have not been clearly elucidated. The molecular mechanism of albumin's effect on the prognosis of CVD may be multifactorial, which may include maintaining vascular endothelial integrity, regulating vasodilation, binding toxins, anticoagulation, and antioxidation, etc. 7 . Burl R Don et al. pointed out that the poor nutritional status reflected by low sALB may also be one of the risk factors of poor prognosis 18 . Studies have pointed out that albumin plays an important role in the transport of serum and cellular cholesterol and the maintenance of cholesterol homeostasis 11,16,19,20 . Albumin can shuttle free cholesterol among various receptors, which will increase the movement of free cholesterol under concentration gradients between the numerous cholesterol pools present in plasma and tissues, thereby promoting and maintaining cholesterol metabolism to restore steady-state levels 20 . The improving of cholesterol efflux may improve the prognosis of CAD 21 . What's more, Deepak Kumar et al. found that the pseudoesterase activity of albumin might be an important determinant of cholesterol biosynthesis 22 . These study results may suggest that the influence of albumin level on the risk of poor prognosis may be closely related to cholesterol level. In conclusion, based on our analysis, we believe that TC level may influence the effect of sALB on the risk of poor prognosis in CAD patients treated by percutaneous coronary intervention. The potential limitations of the current analysis should also be considered in interpreting the study results. First, the data of our study came from a single-center sample, mainly elderly patients with CAD who underwent PCI. Therefore, for the extension of the research conclusions, further research is still needed. Second, the patients with chronic liver diseases, end stage renal diseases, malabsorption disease can effect serum albumin and cholesterol levels, but our data did not include these situation of the participants. Thus, we do not know whether TC affects the association of sALB with MACE in these patients, so our conclusions should be applied with caution in this group of patients. Finally, we have to emphasize that our results are merely hypothesis-generating; confirmation of our findings in an independent randomized trial is essential.

Method
Research design and population. This was a secondary scientific analysis of a retrospective, singlecenter cohort study where the dataset was collected by Sho et al. and is now available on Dryad (via:https:// doi. org/ 10. 5061/ dryad. fn673 0j) 15  www.nature.com/scientificreports/ excluded. All participants were enrolled after the approval of Shinonoi General Hospital Ethics Committee and written informed consent. The research was consistent with the principles outlined in Helsinki Declaration. The outcome was major adverse cardiac events (MACE; defined as all cause mortality, non fatal myocardial infarction, and non fatal stroke). Events were validated by chart review and the median duration of follow-up was 783 days 15 . In our analysis, we included all the cases to revalidate the relationship between the sALB and MACE by adjusting more covariates than the previous research 15 , and more importantly, we tried to find the effects of TC on their association by interaction tests.
Statistical analysis. The baseline characteristics of the participants were analyzed and divided into two groups according to the median baseline sALB level. The continuous variables with normal distribution were   www.nature.com/scientificreports/ presented as Mean ± SD (comparison between groups by t test), the continuous variables with abnormal distribution were presented as Median (IQR) (comparison between groups by Kruskal Wallis rank sum test) and the categorical variables were presented as N (%) (comparison between groups by χ 2 test). The primary outcome was to determine the effect of TC on the association between MACE and baseline sALB level. Therefore, the results of unadjusted and adjusted covariates model analysis were presented based on STROBE recommendations. When the covariate was included or excluded from the model, the hazard ratio of the match was changed by at least 10%, and this covariate needed to be adjusted 23 . Besides, if it was related to serum albumin and MACE in clinical practice, covariate wound be included with other congener covariates excluded. Moreover, covariates adjusted in previous congener studies were also included 24 . And finally we adjusted, if not stratified, for age, sex, BMI, TC, eGFR, ALT in the multivariable model.
In the multivariable regression analysis, baseline sALB level was first analyzed as a continuous variable and then divided into two groups according to the median level. Interaction tests were conducted according to TC (< 200 mg/dL and ≥ 200 mg/dL), and the models were divided into crude model and adjusted model according to the adjusted covariates. P values less than 0.05 (two-tailed) were considered statistically significant. EmpowerStats ver.3.0 (http:// www. empow ersta ts. net/ analy sis/, X&Y Solutions,Inc., Boston, MA) and the R software ver.3.3.1 (http:// www.R-proje ct. org/, The R Foundation), were used for all statistical analyses.

Data availability
The dataset was collected by Sho et al. and is now available on Dryad (via: https:// doi. org/ 10. 5061/ dryad. fn673 0j). The datasets generated or analysed during the current study are available from the corresponding author on reasonable request.